1. Field of the Invention
The present invention is generally related to an exhaust system and, more particularly, to an exhaust system for a marine propulsion device in which an integral moisture trap is formed in the walls of an exhaust system component so that condensation is trapped in a reservoir for later evaporation and removal when the exhaust system reaches its normal operating temperatures.
2. Description of the Prior Art
It is well known that water can condense within or flow into the exhaust system of a marine propulsion device. The condensation can flow, under the influence of gravity, into an exhaust manifold and then toward the exhaust valves of an internal combustion engine. This condensation can be harmful to an internal combustion engine.
Those skilled in the art of marine propulsion systems are aware of several devices that have been developed to address the problem of water condensation in exhaust components.
U.S. Pat. No. 5,133,185, which issued to Gilbreath et al. on Jul. 28, 1992, describes an anti-moisture device for an engine exhaust. The device is intended to remove moisture droplets from an interior surface of a duct, characterized by an outer edge secured to the interior surface of the duct, an inner edge surrounding an opening, and a connecting wall between the outer edge and inner edge. The inner edge of the anti-moisture device is positioned closer to a downstream end of the duct than the outer edge whereby the connecting wall is positioned at an angle relative to the interior surface of the duct. Moisture droplets traveling upstream will be caught between the connecting wall and the interior surface of the duct, on the downstream side of the device. The connecting wall is dimensioned so that a turbulent disturbance will be created along the interior surface of the duct whereby moisture droplets will be removed. The anti-moisture device is preferably made of a thermally conductive material so that moisture droplets contacting the device will be flashed into steam, or vaporized.
U.S. Pat. No. 6,652,337, which issued to Logan et al. on Nov. 25, 2003, discloses an exhaust system for a marine propulsion engine. The invention provides a relationship between the exhaust passages and coolant passages of the exhaust manifold and exhaust elbow which serves to maintain the joint of the exhaust passage at a higher temperature than would be possible with known exhaust manifolds and exhaust elbows. By providing a space between the surfaces of a raised exhaust portion of the components and surfaces of the raised coolant portions of the exhaust system, leakage from the coolant conduits to the exhaust cavities is avoided. The space provided between the exhaust portions of the manifold and elbow and coolant portions of the manifold and elbow, near the joint between these components, provides the two advantages of maintaining a higher exhaust connection between the manifold and elbow and also preventing coolant leakage from flowing from the coolant passages to the exhaust passages of the exhaust system.
U.S. Pat. No. 6,478,645, which issued to Allbright et al. on Nov. 12, 2002, describes a moisture migration inhibitor for wet marine exhausts. A moisture inhibitor system for wet exhausts as utilized in marine applications, such as boats and other watercraft, is described. The preferred embodiment of the invention contemplates an exhaust manifold having an inner exhaust passage which has situated therein a collection barrier or raised pocket situated to collect moisture migrating from the exhaust port, generally at the stern of the vessel. The collection pocket is heated by the exhaust stream and is formed to collect and retain the migrating moisture while simultaneously the heated walls of the collection barrier evaporate the collected moisture forming moisture vapor which moisture vapor is urged through the exhaust passage and the exhaust port, where it leaves the system. The system thereby prevents moisture migrating up the exhaust passage from reaching the engine. In the preferred embodiment of the invention, the exhaust pipe includes a generally vertical portion emanating from the engine and an elbow at the top of the vertical portion communicating with an exhaust conduit situated generally horizontally, but with a slightly downwardly angled path leading to the exhaust port at the stem of the vessel. In this embodiment, the moisture collection pocket is situated in the lower inner portion of the generally horizontal exhaust conduit, in the vicinity of the elbow. The collection pocket is configured so as to provide minimal disturbance in the flow of exhaust through the system. An alternative embodiment of the device contemplates a moisture collection pocket formed inside portion of the manifold elbow near the manifold opening at the engine head.
U.S. Pat. No. 5,590,523, which issued to Fox on Jan. 7, 1997, describes a flow focusing and mixing device. The invention is a flow focusing and mixing device for use with internal combustion engines. The flow focusing and mixing device may be located in the exhaust stream of an internal combustion engine for increased oxidization of the exhaust, increasing the air quality of the exhaust released into the environment.
U.S. Pat. No. 6,648,338, which issued to Jaeger et al. on Nov. 18, 2003, discloses an exhaust gasket with individually sealed water passages. The gasket is for use with an exhaust system and comprises a metallic plate having an exhaust sealing segment and a coolant sealing segment which is attached to and extends from the exhaust sealing segment. Both segments have first and second planar surfaces on opposite sides thereof, with the first and second planar surfaces of the exhaust sealing segment being coplanar with the first and second planar surfaces of the coolant sealing segment, respectively. An exhaust opening is formed through the plate and first and second elastomeric seals, which can be silicone rubber and which are both integral parts of a common elastomeric element, are disposed on the first and second surfaces, respectively, of the cooling sealing segment. A raised portion of the exhaust opening through the metal plate extends at an angle from the exhaust sealing segment and away from the first surface to form a transition segment from the first opening to a second. A hole can be formed through the plate and located at a central region of the coolant sealing segment with the common elastomeric element extending through the hole with the first and second elastomeric seals being joined to each other within the hole. A central portion of the coolant sealing segments can either comprise a hole to allow liquid to flow through the thickness of the plate, or alternatively, can comprise a solid portion that inhibits a flow of liquid through the thickness of the plate.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
Known solutions to the problem of condensation on the walls of an exhaust system typically require assembly of a number of parts, such as the device described in U.S. Pat. No. 5,133,185. This requires additional expense and assembly time during the manufacture of a marine propulsion system. In addition, concepts similar to the ones described in U.S. Pat. Nos. 5,133,185 and 6,478,645 can adversely affect the efficient flow of exhaust gases through the various conduits of the exhaust system. By protruding into the exhaust gas stream, the overall efficiency of the engine operation can be deleteriously affected. It would therefore be significantly beneficial if a system could be provided for a marine engine exhaust which does not adversely affect the efficiency of flow of exhaust gases through the exhaust system and, additionally, which does not require separate components to be assembled in conjunction with the conduits of the exhaust system.